fix off-by-one error in generic memory scanner for the list GC

Author: niaow

src/runtime/gc_list_generic.go

@@ -8,7 +8,7 @@ import "unsafe"
 func markMem(start, end uintptr) {
 	start = align(start)
 	end &^= unsafe.Alignof(unsafe.Pointer(nil)) - 1
-	for ; start < end; start += unsafe.Alignof(unsafe.Pointer(nil)) - 1 {
+	for ; start < end; start += unsafe.Alignof(unsafe.Pointer(nil)) {
 		markAddr(*(*uintptr)(unsafe.Pointer(start)))
 	}
 }